The Dacian Wars were two short but violent wars fought by Trajan, Emperor of the Roman Empire from 98 to 117 A.D. Less than forty years earlier, in 64 A.D., Nero had begun issuing coins with a lower percentage of gold in them, thus initiating a downward spiral of inflation. However, the region of Dacia (more or less located around modern-day Romania, on the other side of the Danube River from the Roman Empire), had a sizeable supply of gold from mines in the Carpathian Mountains. Trajan had heard about this and wanted to boost the treasury and the faltering standard of currency. He was also worried about the Dacians becoming too strong of a neighbor, as they had been raiding on his border along the Danube for quite some time. For these two reasons, he attacked Dacia in 101 A.D., justifying his move against Dacia initially because of the raids.

The Dacians really had no chance against the efficient military expertise of Trajan and his legions. By 102 A.D., the Romans had significantly defeated the Dacians at a place called Topae, as well as damaging several other settlements, and were on their way toward the capital, Sarmizegetusa. To placate the Romans, the Dacian king, Decebalus, accepted a peace treaty. In order to reduce the threat of the Dacians on his border, Trajan demanded that they dismantle their fortifications along the Danube River as one of the treaty's conditions.

Not content with this, Trajan declared Decebalus to be in violation of the treaty in 105 A.D., and marched against Dacia for a second time when the Dacians tried to attack across the Danube again that summer. Trajan defeated them just as easily as before and forced Decebalus back to the capital. After the Romans had besieged Sarmizegetusa for some time, Decebalus tried to escape the city for the nearby Carpathian Mountains to organize a resistance. However, Roman cavalry chased them down and captured them, but not before Decebalus chose to commit suicide rather than be captured, leaving Dacia in the hands of the Romans. Dacia then became a Roman province until 271 A.D., when the Roman soldiers occupying the territory left.

There were two monumental projects built as a result of the Dacian Wars. The first was a huge bridge, 3300 feet long, built across the Danube River near a place called Drobetae in 104 A.D. in preparation for the second assault. It was designed by Trajan's primary architect, Apollodorus of Damascus. He also designed the other project, the Forum of Trajan with its magnificent column, which contains a frieze in a continuous spiral showing the Dacian campaign in carved relief. To further uplift his deeds and impress the people, Trajan originally had a statue of himself placed on top of this column.

The Dacian campaign was the last successful campaign waged by the Roman Empire, successful in the sense of both conquering new land and profiting from the spoils of the conquest. Not too much is known about it compared to most of the many other wars in Roman history, but it certainly had a Romanizing effect on the culture of the people who were to become Romanians, and it resulted in one of the most impressive pieces of art from the Roman Empire.

Sources:
http://members.tripod.com/romeartlover/Romanwar.html
http://www.transylvania.be/istorie_eng1.html
http://nis-www.lanl.gov/~ctr/trajan_catalog.html